It's a guess, but based on tradition and some chatter that I picked up off of SportsCenter. Everybody says that Stanford has a great team this year, and they will likely win whichever game they end up in. But the team doesn't travel well, so they aren't expected to get picked by the bowls that get first pick. The Rose Bowl will have the option of Stanford or TCU, and all signs point to them taking TCU.
There is a new clause in the Rose contract that they have to periodically take a team from outside of the auto-qualify conferences. They could take care of that obligation by taking #3 TCU this year and then they are good for three or four years.